8 ZOOLOGY. 



toes are short, and the remaining parts long ; for 

 instance, one of the tarsal bones, the_ calcaneum 

 (heel-bone), is strongly developed and projects behind 

 (28 *). In the hand, the digits are relatively long, 

 and since the tip of the thumb can be made to touch 

 the tips of all the fingers, are admirably adapted for 

 grasping. 



The number of fingers or toes is at most five, but 

 may be less. The horse has a single digit to each 

 limb ; the ox, two well developed and two remaining 

 as rudiments ; the pig, two large and two small ; while 

 the dog has four toes in the hind foot, five in the fore 

 foot. 



Man walks on the sole of the foot. Some other 

 animals (dog, cat) on the toes; others again (horse, 

 ox, pig), on the tips of the toes. In the last case 

 there is not simply a horny structure (nail or claw) 

 on the upper side of the toe, but a hoof sheathing the 

 whole of its tip. In many animals the thigh and 

 upper arm are drawn close up to the body, so that 

 the limbs appear quite diiferent from those of man. 

 (Compare Fig. 2 with Fig. 3.) 



The bones are usually surrounded by flesh. This 

 consists of a number of difierent pieces united together 

 by a delicate, elastic, fibrous mass (connective tissue). 

 The difierent pieces are termed Tnuscles, each of which 

 is again made up of a large number of muscle-fibres, 

 all taking a longitudinal direction. Each fibre can 

 contract, and a muscle becomes shorter and thicker 

 by simultaneous contraction of all its fibres. The 

 contraction and subsequent relaxation of muscles 

 move other parts. There are some muscles, the 

 hollow muscles, which surround a cavity, and by their 

 contraction propel the liquid or solid substances found 

 in their cavity. The heart, for example, is a large 

 muscle of this sort, serving to propel the blood, while 

 the hollow muscular coat of the gut moves on the con- 

 tained food. Other muscles are fixed by their ends 



